The invention relates to a microbial process for the enantioselective reduction of keto compounds of the formula I EQU R.sup.3 HN--CHR.sup.1 --CO--CH.sub.2 --COOR.sup.2 I
in which
R.sup.1 is A, Ar, Ar-alkyl, Het, Het-alkyl, cycloalkyl having 3-7 C atoms which is unsubstituted or mono- or polysubstituted by A, AO and/or Hal, cycloalkylalkyl having 4-11 C atoms or bicycloalkyl having 7-14 C atoms or bicycloalkylalkyl having 8-18 C atoms,
R.sup.2 is H or alkyl having 1-5 C atoms,
R.sup.3 is H, benzyl, triphenylmethyl, benzyloxycarbonyl, tert.-butyloxycarbonyl or 9-fluorenylmethoxycarbonyl,
Ar is phenyl which is unsubstituted or mono- or polysubstituted by A, AO, Hal, CF.sub.3, HO, hydroxyalkyl having 1-8 C atoms, H.sub.2 N and/or aminoalkyl having 1-8 C atoms or is unsubstituted naphthyl,
Het is a saturated or unsaturated 5- or 6-membered heterocyclic radical having 1-4 N, O and/or S atoms which can be fused with a benzene ring and/or mono- or polysubstituted by A, AO, Hal, CF.sub.3, HO, O.sub.2 N, carbonyl oxygen, H.sub.2 N, HAN, A.sub.2 N, AcNH, AS, ASO, ASO.sub.2, AOOC, CN, H.sub.2 NCO, HOOC, H.sub.2 NSO.sub.2, ASO.sub.2 NH, Ar, Ar-alkenyl, hydroxyalkyl and/or aminoalkyl each having 1-8 C atoms and/or whose N and/or S heteroatoms can also be oxidized,
Hal is F, Cl, Br or I,
Ac is A--CO--, Ar--CO-- or A--NH--CO-- and
A is alkyl having 1-8 C atoms, to give the corresponding secondary alcohols which are important intermediates in the synthesis of pharmacologically useful renin inhibitors.